Driving power of a wheel loader engine is divided to two power transmission paths, namely drive and working power transmission paths. This means that the driving power of the engine is supplied to a drive power train and a work machine hydraulic pump via a PTO shaft to be divided into drive horsepower and work horsepower.
An input clutch (modulation clutch) is provided between the engine and the transmission in the power transmission path of the drive power train.
The input clutch is provided for adjusting the power transmitted to the drive power train to increase the power transmitted to the work machine via the work machine hydraulic pump according to a work condition or to prevent the vehicle from slippage.
In order to cause the wheel loader to dig the ground to do an excavation work, the operator is required to decrease the speed of the vehicle body while depressing an accelerator pedal to keep the engine speed high. Therefore, the operator depresses a brake pedal to actuate a brake to decrease the speed of the vehicle body. At the same time, the clutch pressure of the input clutch is decreased to enhance the braking effectiveness, while the engine driving power transmitted to the drive power train is decreased to increase the amount of driving power allocated to the work machine hydraulic pump by that much.
Patent Publication 1 specified below describes an invention according to which a signal corresponding to a depression amount of the brake pedal is transmitted to a control valve for controlling the input clutch to actuate the control valve, and the clutch pressure of the input clutch is adjusted by the control valve to decrease the input clutch pressure according to the brake pedal depression amount.
Patent Publication 1: Published Japanese Translation of PCT Publication for a Patent Application-(Toku Kohyou) NO. 5-502834